VSWR alarm system

ABSTRACT

There is disclosed herein a VSWR alarm system which produces an alarm when an undesired VSWR is present on a transmission line. The alarm system includes a directional coupler to detect the forward voltage and reflected voltage on the transmission line. An amplifier amplifies the reflected voltage by a given value dependent upon the desired VSWR. An amplitude comparator employs the amplitude of the forward voltage as a reference voltage and compares the amplitude of the amplified reflected voltage to this reference voltage. When the amplitude of the amplified reflected voltage is greater than the amplitude of the reference voltage, an alarm indication is produced. The production of the alarm indication can only produce an alarm when there is transmitting energy on the transmission line due to a NAND gate coupled to a transmitter logic circuitry and the amplitude comparator. A storage device is coupled to the output of the NAND gate and provides a VSWR alarm when the alarm indication is present in the storage device. A fault lamp is activated and an alarm is produced when the storage device stores the alarm indication. A timing circuit responsive to the activation of the fault lamp is employed to reset the storage means after a given time interval.

Ftpaioz I XR United States Patent [1 1 Straw 1 Mar. 11, 1975 1 VSWR ALARM SYSTEM [75] Inventor: Richard D. Straw, San Francisco,

Calif.

International Telephone and Telegraph Corporation, Nutley, NJ.

[22] Filed: Oct. 15, 1973 [21] Appl. No.: 406,711

[73] Assignee:

317/43; 330/207 R, 207 P; 307/202 R, 203, 207; 328/8; 340/253 R, 253 A, 253 C, 253 D, 253 O; 333/17 R 3,508,115 4/1970 Drushel 340/253 A 3,659,214 4/1972 lijima r 328/8 3,794,941 2/1974 Templin 333/17 Primary ExaminerBenedict V. Safourek Attorney, Agent, ,or Firm-John T. Ol-lalloran; Menotti .1. Lombardi, Jr.; Alfred C. Hill [57] ABSTRACT There is disclosed herein a VSWR alarm system which produces an alarm when an undesired VSWR is present on a transmission line. The alarm system includes a directional coupler to detect the forward voltage and reflected voltage on the transmission line. An amplifier amplifies the reflected voltage by a given value dependent upon the desired VSWR. An amplitude comparator employs the amplitude of the forward voltage as a reference voltage and compares the amplitude of the amplified reflected voltage to this reference voltage. When the amplitude of the amplified reflected voltage is greater than the amplitude of the reference voltage, an alarm indication is produced. The production of the alarm indication can only produce an alarm when there is transmitting energy on the transmission line due to a NAND gate coupled to a transmitter logic circuitry and the amplitude comparator. A storage device is coupled to the output of the NAND gate and provides a VSWR alarm when the alarm indication is present in the storage device. A fault lamp is activated and an alarm is produced when the storage device stores the alarm indication. A timing circuit responsive to the activation of the fault lamp is employed to reset the storage means after a given time interval.

13 Claims, 1 Drawing Figure ANTENNA srnao; LEGEND ID: NAND car:

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hmxuwimk k m Hnt ' 1 VSWR ALARM SYSTEM BACKGROUND OF THE INVENTION The present invention relates to a voltage standing wave ratio (VSWR) alarm system.

SUMMARY OF THE INVENTION An object of the present invention is to provide a VSWR alarm system to produce an alarm when an undesired VSWR is present on a transmission line.

Another object of the present invention is to provide a VSWR alarm system suitable for manufacturing by integrated circuit techniques.

A feature of the present invention is the provision of a voltage standing wave ratio alarm system comprising: first means to detect a forward voltage and a reflected voltage on a transmission line; second means coupled to the first means to amplify the reflected voltage by a given value dependent upon the desired voltage standing wave ratio; and third means coupled to the first means and the second means to compare the amplitude of the amplified reflected voltage to the amplitude of the forward voltage and to produce an .alarm indication when the amplitude of the amplified reflected voltage is greater than the amplitude of theforward voltage Another feature of the present invention is the provision in addition to the above-mentioned means of a fourth means that enables production of an alarm from the alarm indication only when a transmitter associated with the alarm system is transmitting on the transmission line.

Still another feature of the present invention is the provision in addition to the above-mentioned means of a fifth means coupled to the output of the third means to store the alarm indication and provide a VSWR alarm when the alarm indication is present in the fifth means; sixth means coupled to the fifth means to activate a fault lamp; and seventh means coupled to the fifth means and the sixth means, the seventh means being activated in response to activation of the fault lamp to reset the fifth means after a given time interval.

BRIEF DESCRIPTION OF THE DRAWING Above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawing, the sole FIGURE of which is a schematic diagram of the VSWR alarm system in accordance with the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The VSWR alarm system of the present invention is incorporated in a transceiver employing an automatic tuning circuit for an antenna coupler disposed between an antenna and the power amplifier of a transmitter. The details of the automatic antenna coupler tuning circuit is disclosed in the copending application of R. D. Straw Ser. No. 407,325, filed Oct. 17, 1973, which is incorporated herein by reference. The VSWR alarm system of the present invention is interconnected with the automatic antenna coupler tuning circuit to cooperate with the radio frequency (RF) output indicating portion of the automatic antenna coupler tuning circuit.

Referring to the FIGURE, the VSWR alarm system includes a directional coupler l to produce a forward voltage E, on transmission line 2, illustrated to be a coaxial transmission line, and also a reflected voltage E, present on transmission line 2. The magnitude of the forward and reflected voltages are related to the VS WR by the following relationship:

For a certain desired value of VS WR there is a fixed ratio of E, to E as can be seen if the above equation is rewritten as:

- For a VSWR of two, the ratio of E, to E, is 15, or in other words, E, is three times the value of E,. Similarly, the ratio of E, to E; is l for a VSWR of three.

Whatever the actual values of the forward and reflected voltages, their ratio determines the VSWR. If the forward voltage is used to set the reference voltage on a comparator, when the reflected voltage. multiplied by a given gain of A, is equal to or greater than the comparators reference voltage, the comparator will be turned on, indicating the VSWR is greater than or equal to A. This will hold true regardless of power level as long as the detectors 3 and 4 in the directional coupler 1 remain linear. Operational amplifiers 5 and 6 are used to amplify the forward and reflected output voltages from coupler 1 by a factor of three. The pur-.

pose of these amplifiers 5 and 6 is to ensure reliable operation of the Schmidt trigger circuit employed in the RF output indicating portion of the automatic antenna coupling tuning circuit of the above-cited copending application. The gain of amplifiers 5 and 6 is not necessary for the VSWR alarm operation.

The reflected voltage at the output of amplifier 6 is amplified by operational amplifier 7 by a factor of three for a VSWR equal to 2/1 or by a factor of two for a VSWR equal to 3/1. Depending upon which of these desired VSWRs are to be present on transmission line 2, the gain of operational amplifier 7 is set by the ratio of the series pair of resistor R1 and R2 to resistor R3, in other words, by the ratio (R1 R2)/R3. The gain of amplifier 7 is adjusted by resistor R2 for a VSWR trip point of either 2 to l or 3 to 1 depending upon the desired VSWR in transmission line 2. Diode 8, capacitor C1 and resistor R4 form a fast-attack, slow-decay circuit to help prevent transients from falsely actuating the alarm. Diode 9, resistor R5 and capacitor C2 in the path for the forward voltage also serve this same function. The function of R6 is to provide a very small source of positive voltage on the inverting input 10 of operational amplifier 11 to prevent any ambiguity when RF is not present in transmission line 2, in other words, when both the forward voltage and reflected voltage are zero. i

Let us assume that the desired VSWR is 2 to l. The gain of amplifier 7 will be set by resistor R2 to provide a gain of three in amplifier 7. If the VSWR is greater than 2 to 1 the non-inverting input 12 of amplifier 11 will be higher than inverting input 10 and the output of amplifier 11 will go high. If the fault lasts long enough, capacitor C3 is charged through resistor R7 and turns on transistor 13. The low pass filter formed by resistor 7 and capacitor C3 also serve to prevent transients from falsely actuating the alarm.

If the transmitter has gone to the ready state (that is, has been tuned) input 14 of NAND gate 15 will be low. A low received from the VSWR comparator 11 due to inversion in transistor 13 will cause input 16 of gate 15 to go low and the output of gate 15 will go high. The result of a high condition at the output of gate 15 is to set the storage circuit including cross coupled NAND gates 17 and 18 through means of NOT gate 19. The output of NAND gate 17 will go high and transistor 20 will be turned on causing an antenna fault lamp to light for the operator to see on the remote control display panel. In addition, when transistor 20 is turned on the transceiver will be removed from the transmit state by causing the VSWR alarm output line 21 to produce an alarm and thereby command a receive only state for the transceiver. A timer circuit including transistors 22, 23 and 24 is also activated at the time transistor 20 is turned on. The action of the timer circuit is to reset the storage flip flop including gates 17 and 18 after about three seconds. If the fault is still present, the system will again default and go out of the transmit state. This sequence will continue for as long as the fault is present, that is, as long as the desired VSWR is not detected.

The transmitter must be in a ready state before the VSWR alarm is activated because when the antenna is not tuned the VSWR is by definition not correct. Only after the antenna coupler has been tuned as disclosed in the above-cited copending application can the VSWR be correct and less than 2 to l.

The RF output indicating portion of the automatic antenna coupler tuning circuit of the above-cited copending application uses the forward voltage on conductor X connected to the output of amplifier 5 to trigger a Schmidt trigger circuit contained in this RF output indicating system as is fully described in the abovecited copending application.

While I have described above the principles of my invention in connection with specific apparatus it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A voltage standing wave ratio alarm system comprising:

first means to detect a forward voltage and a reflected voltage on a transmission line;

second means coupled to said first means to amplify said reflected voltage by a given value dependent upon the desired voltage standing wave ratio;

third means coupled to said first means and said second means to compare the amplitude of said amplified reflected voltage to the amplitude of said forward voltage and to produce an alarm indication when the amplitude of said amplified reflected voltage is greater than the amplitude of said forward voltage;

a source of transmit ready signal, said transmit ready signal being present at the output of said source only when a transmitter associated with said system is transmitting on said transmission line; and

fourth means coupled to said third means and said source responding to the simultaneous presence of said transmit ready signal and said alarm indication to produce an alarm.

2. A system according to claim 1, further including fifth means coupled between said first means and said third means to amplify said forward voltage by a predetermined amount; and sixth means coupled between said first means and said second means to amplify said reflected voltage said predetermined amount. 3. A system according to claim 2, wherein each of said fifth and sixth means includes an operational amplifier having a gain equal to said predetermined amount. 4. A system according to claim 1, further including fifth means coupled to the output of said third means to store said alarm indication and provide a voltage standing wave ratio alarm when said alarm indication is present in said fifth means; sixth means coupled to said fifth means to activate a fault lamp; and seventh means coupled to said fifth means and said sixth means, said seventh means being activated in response to activation of said fault lamp to reset said fifth means after a given time interval. 5. A system according to claim 4, wherein said first means includes a directional coupler coupled to said transmission line to detect said forward and reflected voltage. 6. A system according to claim 4, wherein said second means includes an operational amplifier having an adjustable gain to amplify said reflected voltage by said given value. 7. A system according to claim 4, wherein said third means includes an operational amplifier coupled to said first means and said second means to operate as an amplitude comparator, said forward voltage being em ployed as a reference voltage by said operational amplifier. 8. A system according to claim 4, wherein said fourth means includes a NAND gate responding to the simultaneous presence of said alarm indication and said transmit ready signal from said source. 9. A system according to claim 4, wherein said fifth means includes a pair of cross coupled NAND gates coupled to the output of said fourth means. 10. A system according to claim 4, wherein said sixth means includes a transistor having its base coupled to the output of said fifth means, its emitter grounded and its collector coupled to said fault lamp. 11. A system according to claim 4, wherein said seventh means includes a timer circuit having three interconnected transistors coupled between the output of said sixth means and a reset input of said fifth means. 12. A system according to claim 4, wherein said first means includes a directional coupler coupled to said transmission line having a first output providing said forward voltage and a second output providing said reflected voltage; said second means includes a first operational amplifier having an adjustable gain to amplify said reflected voltage by said given value and having its nominverting input coupled to said second output of said directional coupler; said third means includes a second operational amplifier having its inverting input coupled to said first output of said directional coupler and its non-inverting input coupled to the output of said first operational amplifier;

said fourth means includes a first two input NAND gate having one of its inputs coupled to the output of said second operational amplifier and its other input coupled to said source of said transmit ready signal so that said alarm is produced only during the simultaneous presence of said transmit ready signal and said alarm indication;

said fifth means includes a second two input NAND gate,

a third two input NAND gate having one input connected to the output of said second NAND gate and an output to provide said alarm when said alarm indication and said transmit ready signal are present, said output of said third NAND gate being connected to one input of said second NAND gate, and

the other input of said second NAND gate being connected to the output of said first NAND gate;

said sixth means includes a first transistor having its base connected to the output of said second NAND gate, its emitter grounded and its collector coupled to said fault I lamp; and

said seventh means includes a timer circuit having a second transistor with its base coupled to the collector of said first transistor and its emitter grounded,

a third transistor with its emitter connected to the collector of said second transistor, its base connected to the other input of said third NAND gate, and

a fourth transistor with its base connected to the collector of said third transistor, its emitter grounded and its collector connected to the other input of said third NAND gate.

13. A system according to claim 12, further including a third operational amplifier having its non-inverting input coupled to said first output of said directional coupler and its output coupled tothe inverting input of said second operational amplifier, said third operational amplifier amplifying said forward voltage by a predetermined amount; and

a fourth operational amplifier having its noninverting input coupled to said second output of said directional coupler and its output coupled to the non-inverting input of said second operational amplifier, said fourth operational amplifier amplifying said reflected voltage by said predetermined amount. 

1. A voltage standing wave ratio alarm system comprising: first means to detect a forward voltage and a reflected voltage on a transmission line; second means coupled to said first means to amplify said reflected voltage by a given value dependent upon the desired voltage standing wave ratio; third means coupled to said first means and said second means to compare the amplitude of said amplified reflected voltage to the amplitude of said forward voltage and to produce an alarm indication when the amplitude of said amplified reflected voltage is greater than the amplitude of said forward voltage; a source of transmit ready signal, said transmit ready signal being present at the output of said source only when a transmitter associated with said system is transmitting on said transmission line; and fourth means coupled to said third means and said source responding to the simultaneous presence of said transmit rEady signal and said alarm indication to produce an alarm.
 1. A voltage standing wave ratio alarm system comprising: first means to detect a forward voltage and a reflected voltage on a transmission line; second means coupled to said first means to amplify said reflected voltage by a given value dependent upon the desired voltage standing wave ratio; third means coupled to said first means and said second means to compare the amplitude of said amplified reflected voltage to the amplitude of said forward voltage and to produce an alarm indication when the amplitude of said amplified reflected voltage is greater than the amplitude of said forward voltage; a source of transmit ready signal, said transmit ready signal being present at the output of said source only when a transmitter associated with said system is transmitting on said transmission line; and fourth means coupled to said third means and said source responding to the simultaneous presence of said transmit rEady signal and said alarm indication to produce an alarm.
 2. A system according to claim 1, further including fifth means coupled between said first means and said third means to amplify said forward voltage by a predetermined amount; and sixth means coupled between said first means and said second means to amplify said reflected voltage said predetermined amount.
 3. A system according to claim 2, wherein each of said fifth and sixth means includes an operational amplifier having a gain equal to said predetermined amount.
 4. A system according to claim 1, further including fifth means coupled to the output of said third means to store said alarm indication and provide a voltage standing wave ratio alarm when said alarm indication is present in said fifth means; sixth means coupled to said fifth means to activate a fault lamp; and seventh means coupled to said fifth means and said sixth means, said seventh means being activated in response to activation of said fault lamp to reset said fifth means after a given time interval.
 5. A system according to claim 4, wherein said first means includes a directional coupler coupled to said transmission line to detect said forward and reflected voltage.
 6. A system according to claim 4, wherein said second means includes an operational amplifier having an adjustable gain to amplify said reflected voltage by said given value.
 7. A system according to claim 4, wherein said third means includes an operational amplifier coupled to said first means and said second means to operate as an amplitude comparator, said forward voltage being employed as a reference voltage by said operational amplifier.
 8. A system according to claim 4, wherein said fourth means includes a NAND gate responding to the simultaneous presence of said alarm indication and said transmit ready signal from said source.
 9. A system according to claim 4, wherein said fifth means includes a pair of cross coupled NAND gates coupled to the output of said fourth means.
 10. A system according to claim 4, wherein said sixth means includes a transistor having its base coupled to the output of said fifth means, its emitter grounded and its collector coupled to said fault lamp.
 11. A system according to claim 4, wherein said seventh means includes a timer circuit having three interconnected transistors coupled between the output of said sixth means and a reset input of said fifth means.
 12. A system according to claim 4, wherein said first means includes a directional coupler coupled to said transmission line having a first output providing said forward voltage and a second output providing said reflected voltage; said second means includes a first operational amplifier having an adjustable gain to amplify said reflected voltage by said given value and having its non-inverting input coupled to said second output of said directional coupler; said third means includes a second operational amplifier having its inverting input coupled to said first output of said directional coupler and its non-inverting input coupled to the output of said first operational amplifier; said fourth means includes a first two input NAND gate having one of its inputs coupled to the output of said second operational amplifier and its other input coupled to said source of said transmit ready signal so that said alarm is produced only during the simultaneous presence of said transmit ready signal and said alarm indication; said fifth means includes a second two input NAND gate, a third two input NAND gate having one input connected to the output of said second NAND gate and an output to provide said alarm when said alarm indication and said transmit ready signal are present, said output of said third NAND gate being connected to one input of said second NAND gate, and the other input of sAid second NAND gate being connected to the output of said first NAND gate; said sixth means includes a first transistor having its base connected to the output of said second NAND gate, its emitter grounded and its collector coupled to said fault lamp; and said seventh means includes a timer circuit having a second transistor with its base coupled to the collector of said first transistor and its emitter grounded, a third transistor with its emitter connected to the collector of said second transistor, its base connected to the other input of said third NAND gate, and a fourth transistor with its base connected to the collector of said third transistor, its emitter grounded and its collector connected to the other input of said third NAND gate. 